Integrated sensors

ABSTRACT

Examples of integrated sensors are disclosed herein. An example of an integrated sensor includes a substrate and a sensing member formed on a surface of the substrate. The sensing member includes collapsible signal amplifying structures and an area surrounding the collapsible signal amplifying structures that enables self-positioning of droplets exposed thereto toward the collapsible signal amplifying structures.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made in the course of research partially supported bygrants from the Defense Advanced Research Projects Agency (DARPA),Contract No. HR0011-09-3-0002. The U.S. government has certain rights inthe invention,

BACKGROUND

Assays and other sensing systems have been used in the chemical,biochemical, medical and environmental fields to detect the presenceand/or concentration of one or more chemical species. Some sensingtechniques utilize color or contrast for species detection andmeasurement, including, for example, those techniques based uponreflectance, transmittance, fluorescence, or phosphorescence. Othersensing techniques, such as Raman spectroscopy or surface enhanced Ramanspectroscopy (SERS), study vibrational, rotational, and otherlow-frequency modes in a system. In particular, Raman spectroscopy isused to study the transitions between molecular energy states whenphotons interact with molecules, which results in the energy of thescattered photons being shifted. The Raman scattering of a molecule canbe seen as two processes. The molecule, which is at a certain energystate, is first excited into another (either virtual or real) energystare by the incident photons, which is ordinarily in the opticalfrequency domain. The excited molecule then radiates as a dipole sourceunder the influence of the environment in which it sits at a frequencythat may be relatively low (i.e., Stokes scattering), or that may berelatively high (i.e., anti-Stokes scattering) compared to theexcitation photons. The Raman spectrum of different molecules or mattershas characteristic peaks that can be used to identify the species,

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of examples of the present disclosure willbecome apparent by reference to the following detailed description anddrawings, in which like reference numerals correspond to similar, thoughperhaps not identical, components. For the sake of brevity, referencenumerals or features having a previously described function may or maynot be described in connection with other drawings in which they appear.

FIGS. 1A and 1B are semi-schematic, perspective views of an example ofan integrated sensor prior to and after exposure to a liquid sample;

FIGS. 2A through 2E are semi-schematic, top views of five differentexamples of predetermined geometric shapes of controllably positionedcollapsible signal amplifying structures;

FIGS. 3A through 3C are semi-schematic, perspective views of threedifferent examples of a collapsible signal amplifying structure;

FIGS. 4A through 4D are semi-schematic, perspective views which togetherillustrate an example of a method for making an integrated sensor, andwhich also include two cross-sectional views at the arrows between FIGS.4A and 4B and between FIGS. 4B and 4C;

FIG. 5 is a semi-schematic, top view of a sensing member includingcollapsible signal amplifying structures surrounded by a gradient ofpolymer nano-pillars;

FIG. 6 is a semi-schematic, top view of a sensing member includingcollapsible signal amplifying structures surrounded by hydrophobicmolecules;

FIG. 7 is a semi-schematic, top view of a sensing member includingcollapsible signal amplifying structures surrounded by grooves;

FIG. 8 is a semi-schematic and partially perspective view of an exampleof a sensing system; and

FIG. 9 is a schematic and partially perspective view of another exampleof a sensing system.

DETAILED DESCRIPTION

The present disclosure relates generally to integrated sensors. Examplesof the integrated sensors are suitable for use in surface enhanced Ramanspectroscopy (SERS). Examples of the sensors include one or more sensingmembers that include collapsible or reconfigurable signal amplifyingstructures arranged in polygon assemblies. The collapsible signalamplifying structures of a single polygon assembly are able to undergoself-coalescence (e.g., self-closing or self-reconfiguration at theirtips), with the aid of capillary forces (e.g., during liquidevaporation). The signal amplifying structures are able to trapmolecules at hot spots formed among the closed tips, which greatlyamplifies electromagnetic fields under SERS interrogation. Additionally,examples of the integrated sensor are controllably formed on flexiblesubstrates, which may advantageously be used for continuous monitoringover long periods of time. Still further, some examples of theintegrated sensor are able to self-position samples exposed thereto,such that the samples are directed toward the collapsible signalamplifying structures. In these examples, the integrated sensors areable to dynamically reconfigure the samples for optimal signalenhancement.

Referring now to FIGS. 1A and 1B, an example of the integrated sensor 10is depicted prior to liquid sample exposure (FIG. 1A) and after liquidsample exposure (FIG. 1B). In an example, the integrated sensor 10includes a flexible substrate 12 and an array of spaced apart sensingmembers 14 _(A), 14 _(B) formed on the surface S₁₂ of the flexiblesubstrate 12. While two sensing members 14 _(A), 14 _(B) are shown inFIGS. 1A and 1B, it is to be understood that any number of sensingmembers 14 _(A), 14 _(B) (also referred to herein as 14) may be formedon the flexible substrate 12. For example, a single sensing member 14_(A) or 14 _(B) may be formed, or tens or hundreds of sensing members 14_(A), 14 _(B) may be formed. The number of sensing members 14 _(A), 14_(B) formed may be limited, for example, by the dimensions (i.e., lengthand width) of the flexible substrate 12 and/or by the number of polygonassemblies 16 formed in any one sensing member 14 _(A), 14 _(B). As someexamples, the array of sensing members 14 _(A), 14 _(B) may include asingle row of sensing members 14 _(A), 14 _(B) along a length of theflexible substrate 12 (see, e.g., FIG. 9), or multiple rows along thelength of the flexible substrate 12 and multiple columns along a widthof the flexible substrate 12 (see, e.g., FIG. 8). The spacing betweenadjacent sensing members 14 _(A), 14 _(B) may depend, for example, uponthe dimensions (i.e., length and width) of the flexible substrate 12and/or the configuration of the dispenser, light source, detector, etc.of a sensing system that will be used to interrogate the sensor 10. Forexample, if the sensing system has a single dispenser for dispensing theanalyte solution (i.e., sample) to the sensing members 14 _(A), 14 _(B),the sensing members 14 _(A), 14 _(B) may be spaced apart a distanceranging from about 1000 μm (i.e., 1 mm) to about 10000 μm (i.e., 10 mm)from one another in a single row along the length of the flexiblesubstrate 12 so that the dispenser can be actuated to fill the sensingmembers 14 _(A), 14 _(B) one after the other. In another example, thedistance between adjacent sensing members 14 _(A), 14 _(B) ranges fromabout 200 μm (0.2 mm) to about 500 μm (0.5 mm) or to about 1000 μm(i.e., 1 mm). A single sensing member 14 _(A), 14 _(B) may have a lengthand/or width ranging from about 0.1 mm to about 2 mm. In an example, asingle sensing member 14 _(A), 14 _(B) may have a length and/or width ofabout 1 mm.

The flexible substrate 12 may be any substrate material that is capableof being flexed or bent without breaking. The flexible substrate 12 isalso capable of having signal amplifying structures 18 formed therein.The flexibility may also enable the flexible substrate 12 to be indexedor moved (e.g., in a continuous manner or a ratcheted manner) formonitoring. Examples of the flexible substrate 12 include polyethyleneterephthalate (PET), polyethylene terephthalate glycol-modified (PETG),polypropylene, polyethylene, or polycarbonate. In an example, theflexible substrate 12 has a thickness that ranges from about 30 μm toabout 50 μm. In other examples, the thickness of the substrate 12 isgreater than 50 μm. In examples in which harder materials are used(e.g., polycarbonate), the thickness of the substrate 12 may be at thelower end of the thickness range in order to obtain the desiredflexibility. The width of some substrates 12 may range from about 8 mmto about 12 mm.

In the example shown in FIGS. 1A and 1B, each sensing member 14 _(A), 14_(B) includes a plurality of polygon assemblies 16 arranged in acontrolled pattern on the surface S₁₂ of the flexible substrate 12. Thecontrolled pattern may include any N×M array, where N, M areindividually selected from 2, 3, 4, 5 . . . 50 . . . 2000. In anexample, N=M=100 to 1000. The controlled pattern of the polygonassemblies 16 shown in each of the sensing members 14 _(A), 14 _(B) ofFIGS. 1A and 1B is a 2×2 array. In this example, each of the sensingmembers 14 _(A), 14 _(B) has the same controlled pattern, but it to beunderstood that one or more of the sensing members 14 _(A), 14 _(B) mayhave the polygon assemblies 16 arranged in a different controlledpattern than one or more of the other sensing members 14 _(A), 14 _(B).Each polygon assembly 16 within a single sensing member 14 _(A) or 14_(B) may be a predetermined distance from each other polygon assembly 16within the same sensing member 14 _(A) or 14 _(B). In an example, thepredetermined distance may range from about 0.5 μm to about 1 μm, or toabout 10 μm. In another example, the predetermined distance may be about0.7 μm. The controlled pattern and the predetermined distance may beobtained using the fabrication methods disclosed herein.

Each polygon assembly 16 includes collapsible signal amplifyingstructures 18 controllably positioned in a predetermined geometricshape. Top views of examples of the predetermined geometric shapes areshown in FIGS. 2A through 2E. These shapes include trigons (i.e., a3-mer, including three collapsible signal amplifying structures 18 asshown in FIG. 2A), teiragons (i.e., a 4-mer, including four collapsiblesignal amplifying structures 18 as shown in FIG. 2B), pentagons (i.e., a5-mer, including five collapsible signal amplifying structures 18 asshown in FIG. 2C), hexagons (i.e., a 6-mer, including six collapsiblesignal amplifying structures 18 as shown in FIG. 2D), and heptagons(i.e., a 7-mer, including seven collapsible signal amplifying structures18 as shown in FIG. 2E). In examples, the period of a polygon assembly16 having a trigon shape or a tetragon shape ranges from about 400 nm toabout 700 nm, and the period of the polygon assembly 16 having apentagon shape, hexagon shape, or heptagon shape ranges from about 600nm to about 900 nm. In an example, an array of polygon assemblies 16 ina single sensing member 14 _(A), 14 _(B) may occupy a space on theflexible substrate 12 that is from about 50 μm to about 100 μm wide andfrom about 50 μm to about 100 μm long. As examples, a 3×3 array ofpentagons may cover an area of about 2×2 μm², while a 30×30 array ofpentagons may cover an area of about 20×20 μm².

It is believed that the controlled fabrication of signal amplifyingstructures 18 in a predetermined geometric shape has not been achieved,at least in part because of the difficulty in obtaining a desired smallgap size (e.g., sub-2 nm gaps between the collapsed signal amplifyingstructures), while also forming substantially uniform structures ofarbitrary symmetry (e.g., tetramers, pentamers, heptamers, etc.) acrossa large area. However, the fabrication methods disclosed herein enableone to control the collapsed gap size as well as the geometry of thepolygon assemblies across a relatively large area (e.g., from about 8 mmto about 12 mm wide).

Each collapsible signal amplifying structure 18 includes a polymer basenano-structure 20 and a signal amplifying material 22 positionedthereon. Examples of the polymer base nano-structures 20 include thepillar, columnar, or finger-like structures shown in FIGS. 1A, 1B and3A, the nanoflake structure shown in FIG. 3B, and the mushroom-shapednano-structure shown in FIG. 3C. As will be described below in referenceto FIGS. 4A through 4D, these polymer base nano-structures 20 are formedin the flexible substrate 12, and thus are formed of the same materialas the flexible substrate 12.

The signal amplifying material 22 may be any material that is capable ofenhancing the signal that is generated during a particular sensingprocess. In an example, the signal amplifying material 22 is a Ramansignal-enhancing material (composition of matter) that increases thenumber of Raman scattered photons when the molecule (or other species ofinterest) is trapped by collapsed signal amplifying structure(s) 18, andwhen the molecule and materials 22 are subjected tolight/electromagnetic radiation. Raman signal-enhancing materialsinclude, but are not limited to, silver, gold, and copper. The signalamplifying material 22 may also be selected for use in other techniques,such as enhanced fluorescence (e.g., metal-enhanced fluorescence orsurface enhanced fluorescence (SEF)) or enhanced chemiluminescence. Asan example, for metal-enhanced fluorescence applications, the polymerbase structures 20 of the signal amplifying structures 18 may be coatedwith silver nanoparticles. Enhanced fluorescence is observed whenincident light couples to the silver nanoparticles with molecules intheir vicinity. The signal amplifying material 22 may be configured tocouple the localized, and in some instances propagating, surfaceplasmons. Methods for depositing the signal amplifying material 22 indesirable positions on the polymer base nano-structures 20 to form thecollapsible signal amplifying structure 18 will also be discussed inreference to FIGS. 4A through 4D.

As illustrated at the arrow between FIGS. 1A and 1B, each of the sensingmembers 14 _(A), 14 _(B) of the integrated sensor 10 of FIG. 1A isexposed to a liquid sample. As shown in FIG. 1B, the collapsible signalamplifying structures 18 that are exposed to the sample undergoself-dosing with the aid of capillary forces, so that the signalamplifying materials 22 are drawn toward one another to create sub nmgaps where analytes of interest (e.g., analyte 24) present in theoriginal liquid sample become trapped. As mentioned above, the dosedsignal amplifying structures 18 form hot spots, which amplify the SERSfields, thereby enhancing the SERS signals.

Referring now to FIGS. 4A through 4D, an example of a method for formingexamples of the integrated sensor 10 is semi-schematically depicted. Themethod is a controlled method based upon nanoimprinting or embossing.FIGS. 4A through 4D describe a method based upon nanoimprinting.Embossing may involve preparing a silicon mold and then using the moldto transfer mold features to a polymer.

FIG. 4A illustrates a perspective view of a mold 26 that may be used toform the polygon assemblies 16 of each sensing member 14 _(A), 14 _(B).The mold 26 shown in FIG. 4A includes a pattern for forming one sensingmember having four polygon assemblies, each of which is a pentagon or5-mer. This is a simplified example of the mold 26, and it is to beunderstood that the mold 26 may have any controlled pattern(s) thatmimics the polygon assemblies to be formed, including the controlledgeometric shape of the polymer base nano-structures 20 of the signalamplifying structures 18 to be formed. For example, when multiplesensing members are to be formed using the mold 26, the mold 26 mayinclude a plurality of spaced apart controlled patterns, each of whichcorresponds to the desired pattern of the respective structures to beformed. The patterns and features of the mold 26 will be used to formthe patterns and features of the final integrated sensor 10. The mold 26may be formed of single crystalline silicon, polymeric materials(acrylics, polycarbonates, polydimethylsiloxane (PDMS), polyimide,etc.), metals (aluminum, copper, stainless steel, nickel, alloys, etc.),quartz, ceramic, sapphire, silicon nitride, or glass.

When multiple sensing members 14, 14 _(A), 14 _(B) are to be formed, themold 26 includes a pattern for the to-be-formed sensing members 14, 14_(A), 14 _(B) (i.e., defining the spacing between sensing members), apattern for the placement of the to-be-formed polygon assemblies 16 ofeach sensing member 14, 14 _(A), 14 _(B), and a pattern for theto-be-formed polymer base nano-structures 20 of each polygon assembly16. In other words, the mold patterns are a replica of the desiredsensing members 14, 14 _(A), 14 _(B) (including the polygon assemblies16) to be formed in the flexible substrate 12.

The patterns may be integrally formed in the mold 26. In an example, thepatterns may be formed in the mold 26 via electron-beam (e-beam)lithography or photolithography, and dry etching. To generate thecontrolled patterns described herein, focused ion-beam or opticallithography may also be used to form the mold 26. The mold may also beprepared by direct etching of a silicon substrate.

The mold 26 is then used to transfer the controlled patterns to a UV orthermal curable resist to form a polymeric reverse-tone mold 28, whichis shown in FIG. 4B. As illustrated, the polymeric reverse-tone mold 28takes on the negative replica of the patterns of the mold 26. In otherwords, the controlled pattern of the polygon assemblies and the polymerbase nano-structures extend into the surface S₂₈ of the polymericreverse-tone mold 28. As such, the curable resist used to form thepolymeric reverse-tone mold 28 is selected to have a sufficient rigidityto be able to conform to, and to duplicate/replicate with precision, thepatterns of the mold 26.

Suitable ultraviolet curable resists for forming the polymericreverse-tone mold 28 include a photoinitiator (i.e., a compound thatgenerates a radical in response to UV radiation exposure), across-linking agent, and a siloxane based backbone chain (e.g., aUV-curable acrylated poly(dimethylsiloxane) material). Examples ofsuitable photoinitiators include azobisisobutyronitrile (AIBN),IRGACURE® 184 and IRGACURE® 810 (commercially available from BASF Corp.,Florham Park, N.J.), and examples of the cross-linking agent includesvarious species having more than one double or triple bond that opens upand polymerizes upon curing. In an example, additional solvents are notincluded in such UV curable resists, at least in part because of thepresence of the siloxane based backbone. The siloxane based backbone mayinclude double bonded terminal functional groups, such as acryls. Thecomponents of the UV resist suitable to form the polymeric reverse-tonemold 28 may be included in a predetermined ratio of photoinitiator tocross-linking agent to siloxane backbone. Each component can be presentin a range of 0.05% to 99.9% of the total weight of the resist. In anexample, the UV resist includes from about 0.5 wt % to about 2 wt % ofthe radical initiator, from about 88 wt % to about 92 wt % of the UVcurable monomer species (i.e., the siloxane based backbone chain), andfrom about 7 wt % to about 11 wt % of the cross-linking agent. Inanother example, the UV resist includes 1 wt % of the radical initiator,90 wt % of the UV curable monomer species (i.e., the siloxane basedbackbone chain), and 9 wt % of the cross-linking agent. Commerciallyavailable resists that may be used for the curable resist includeNXR-2010 (Nanonex Corp., Monmouth Junction, N.J.), and AR-UV-01(Nanolithosolution, Inc., San Marcos, Calif.).

In an example, the polymeric reverse-tone mold 28 may be formed usingultraviolet-curable (i.e., UV-curable) nanoimprint lithography (NIL). AUV-capable NIL tool may be used in this process. The previouslydescribed UV curable resist may be deposited (e.g., via spin coating,drop coating, dip-coating, or the like) onto the mold 26, and then maybe cured (in the tool) to form the polymeric reverse-tone mold 28. Inanother example, the mold 26 may be pressed into the resist that hadbeen previously deposited on a substrate, and then curing is performed.It is to be understood that the curing conditions and parameters willdepend, at least in part, on the UV resist that is used. It is to befurther understood that while the mold 26 is pressed into (or otherwisein contact with) the resist, partial curing may be performed. Partialcuring cures some, but not all, of the resist. After partial curing, themold 26 may be removed. Once the mold 26 is removed, curing may becontinued until the resist is fully cured to form the polymericreverse-tone mold 28.

Prior to depositing the UV curable resist onto the mold 26 or prior topressing the mold 26 into the UV curable resist, the mold 26 may beprimed with a chlorosilane coupling agent (e.g.,3-acryloxypropyl)methyldichlorosilane) that aids in removal of thepolymeric reverse-tone mold 28 from the mold 26 after curing iscomplete. The cross-sectional view shown at the arrow between FIGS. 4Aand 4B illustrates the polymeric reverse-tone mold 28 being removed fromthe mold 26.

The polymeric reverse-tone mold 28 may then be used in anotherUV-curable nanoimprint lithography process (e.g., using the UV-capableNIL tool) to form the polygon assemblies 16 and the associated polymerbase nano-structures 20 in the flexible substrate 12. In this example,the polymeric reverse-tone mold 28 may be pressed into the flexiblesubstrate 12 (as shown at the arrow between FIGS. 4B and 4C), and thencuring may be performed. After curing is complete, the polymericreverse-tone mold 28 may be removed, leaving the flexible substrate 12controllably patterned with polygon assemblies 16 of polymer basenano-structures 20, and thus the sensing members 14,

As shown in FIG. 4D, the signal amplifying material 22 is deposited onat least a surface of the polymer base nano-structures 20 to form thesignal amplifying structure(s) 18. The signal amplifying material 22 maybe established by any suitable deposition or other coating technique. Insome examples, a selective deposition technique may be used so that thematerial 22 is established on, for example, the tips of the basenano-structures 20 alone. As examples, the material 20 may be depositedvia electron-beam (e-beam) evaporation at normal incidence, orsputtering. In still other examples, the signal amplifying material 22can be pre-formed nanoparticles (e.g., of silver, gold, copper, etc.),which are coated onto the polymer base nano-structures 20. Suchnanoparticles may have an average diameter ranging from about 5 nm toabout 50 nm. It is believed that the presence of the material 22 at theapex or tip of the polymer base nano-structures 20 further enhances theelectric field during, e.g., a SERS operation. The material 22 itselfmay also have a surface roughness that spontaneously forms during thedeposition process. This surface roughness can act as additional opticalantennas to increases the SERS-active sites over each signal amplifyingstructure 18. In an example, a thickness of the signal amplifyingmaterial 22 ranges from about 50 nm to about 80 nm.

In the method(s) disclosed herein, since the patterns are preciselydefined in the original mold 26 (e.g., by the initial e-beamlithography) and are faithfully reproducible by nanoimprint lithography,any array of sensing members 14, 14 _(A), 14 _(B) having any controlledpattern of polygon assemblies 16 can be fabricated uniformly atdesirable positions in the flexible substrate 12.

While the method(s) described in reference to FIGS. 4A through 4Dillustrates the formation of metal-capped polymer nano-pillars (e.g.,signal amplifying structures 18), it is to be understood that themethod(s) may also be used to form metal-ringed polymer nano-pillars(shown in FIG. 3A), metal-coated polymer nanoflakes (shown in FIG. 3B),or metal-coated mushroom-shaped nano-structures (shown in FIG. 3C). Toform the metal-ringed polymer nano-pillars, for example, selectivedeposition (e.g., angled deposition) or shadow masking may be used todeposit the signal amplifying material 22 (e.g., preformed material) inthe desired position along the height of the pillar 20. In otherexamples, the metal-ringed polymer nano-pillars may form spontaneouslywhen the signal amplifying material 22 is deposited. To form the polymernanoflakes or mushroom-shaped nano-structures, the original silicon mold26 would be formed in these shapes, as opposed to the pillar shapepreviously described. It is to be understood that these nanoflakes ormushroom-shaped nano-structures may be formed in any of thepredetermined geometric shapes (e.g., trigon, tetragon, etc.) to createthe polygon assemblies 16 of the sensing members 14 _(A), 14 _(B).

It is to be understood that the previously described method(s) may beimplemented as a roll-to-roll process. It is to be further understoodthat the previously described methods may also be modified for thermalimprinting (e.g., using a thermal curable resist) or an embossingprocess.

Referring now to FIGS. 5 through 7, the integrated sensors 10′, 10″, and10′″ includes different examples of the sensing members, respectivelyshown as 14 _(C), 14 _(D), 14 _(E) in these figures. Each of thesesensing members 14 _(C), 14 _(D), 14 _(E) includes an area 30surrounding the collapsible signal amplifying structures 18 that hasbeen modified to enable droplets exposed thereto to position themselvestoward the collapsible signal amplifying structures 18. In other words,the area 30 within a sensing member 14 _(C), 14 _(D), 14 _(E) andsurrounding the controlled pattern of polygon assemblies 16 of thatsensing member 14 may have its surface modified to guide droplets towardthe collapsible signal amplifying structures 18. When the dropletsreposition themselves at the collapsible signal amplifying structures18, analytes within the droplets do not get stuck in the area 30 outsideof or surrounding the collapsible signal amplifying structures 18, andthus are not unaccounted for during sensing. Rather, the droplets arepresent at the area of the sensing member 14 _(C), 14 _(D), 14 _(E) thatcontains the collapsible signal amplifying structures 18. As such, whenthe droplets evaporate down in size (e.g., to about 50 μm to about 100μm in diameter), the concentration of the analyte at the polygonassemblies 16 is increased compared to the initial fluid sample.

As will be described further in reference to FIGS. 5 through 7, themodifications made to the area 30 may be chemical and/or physical.

In the examples shown in FIGS. 5 and 6, the wettability of the area 30is modified. More particularly, the area 30 is modified to be morehydrophobic (i.e., less hydrophilic) than the collapsible signalamplifying structures 18.

In FIG. 5, the area 30 includes a gradient G of polymer pillars withvarying separation between the pillars along the gradient G. Asillustrated in FIG. 5, the gradient G includes polymer pillars 32 thatbecome denser toward the periphery of the sensing member 14. Thegradient G of polymer pillars 32 may be a linear density grade towardsthe collapsible signal amplifying structures 18 so that droplets exposedto the area 30 move from the periphery of the gradient G toward thecollapsible signal amplifying structures 18. The gradient G in FIG. 5includes two different separation sizes (i.e., gaps) between the pillars32, but it is to be understood that the separation size between thepillars 32 may vary more than two times along the gradient G. Thepillars 32 may have a minimum diameter of about 50 nm, which can bescaled up to about 500 nm in a piece-wise linear manner. The 50 nmdiameter pillars 32 may be separated by a distance ranging from about 50nm to about 150 nm, and the 500 nm diameter pillars 32 may be separatedby a distance ranging from about 300 nm to about 500 nm. The scaled updiameters may be anywhere from about 50 nm to about 500 nm, with thedistances between these pillars also ranging from about 50 nm to about500 nm.

The polymer pillars 32 in the area 30 are also free of the signalamplifying material 22.

The polymer pillars 32 may be formed using a mold with the gradienttexture, which can transfer the desired pillar gradient to the area 30.

In FIG. 6, the area 30 is chemically modified by depositing or otherwiseadding a plurality of hydrophobic molecules HPM to the area 30. Anyhydrophobic molecules HPM may be selected, as long as they are morehydrophobic than the collapsible signal amplifying structures 18. Someexamples of the hydrophobic molecules HPM may include (C₂F₂)_(n) chains(e.g., TEFLON®, from DuPont).

In FIG. 7, the area 30 is physically modified with capillary guides orgrooves 34 formed into the surface S₁₂ of the flexible substrate 12. Thecapillary guides or grooves 34 may be embossed into the surface S₁₂ inthe area 30. The shape and dimensions of the capillary guides or grooves34 is selected so that when a droplet is exposed to the capillary guideor groove 34, the droplet automatically moved toward the collapsiblesignal amplifying structures 18. In an example, the capillary guide orgroove 34 is a fraction of a mm long V-groove with a maximum depth of 10μm, where the depth becomes linearly more shallow away from thecollapsible signal amplifying structures 18,

In other examples of the integrated sensor that are not shown, the area30 may include both hydrophobic molecules HPM and capillary guides orgrooves 34, or both hydrophobic molecules HPM and a polymer pillargradient G.

In any of the examples disclosed herein, droplet mobility may beincreased by heating the sensor 10, 10′, 10″, 10′″ or by applying alow-power ultrasound. Heating may be accomplished using an externalheater, or heat from a SERS light source (e.g., reference number 38 inFIGS. 8 and 9) may be suitable for increasing droplet mobility.Low-power ultrasound may be applied using an integrated Si-based PZT((PbZr_(x)Ti_(1-x))O₃) ultrasound transducer. In an example, theultrasound transducer may be integrated into a silicon substrate. Forexample, piezoelectric elements may be formed by the deposition of PZTinto etched features of the silicon substrate. The ultrasound transducermay be operably positioned as a fixed element between the dispenser 36and the light source 38. When the substrate 12 is moved during a sensingoperation, the ultrasound transducer may be operated to excite a samplethat has been dispensed from dispenser 36.

Referring now to FIG. 8, an example of the sensing system 100incorporating an example of the integrated sensor 10 is depicted. Thisexample of the sensor 10 includes multiple sensing members 14 formed infour columns along the width of the flexible substrate 12 and multiplerows along the length of the flexible substrate 12. While not shown forclarity, it is to be understood that each of the sensing members 14includes a controlled pattern of polygon assemblies 16, and may includea modified area 30 as described in reference to FIG. 5, 6 or 7.

In the system 100, the flexible substrate 12 is positioned with respectto the components (e.g., dispenser or dispensing system 36, laser source38, and detector 40) of the sensing system 100 so that dispensing,interrogation, and detection can take place in the desirable order whilethe flexible substrate 12 is indexed past the respective components 36,38, and 40. For example, the flexible substrate 12 may be positionedwith respect to the dispenser 36 so that one or more samples areintroduced onto the sensing member(s) 14 prior to interrogation anddetection. The dispensing system 36 may dispense samples to one or moreof the sensing members simultaneously (e.g., each member 14 in a singlerow may receive a sample simultaneously) and/or sequentially (e.g., onesensing member 14 receives a sample at a time, or one row receives asample at a time, etc.). Examples of the dispensing system 36 includeautomated dispensers based upon inkjet technology, pipetting, or thelike. Manual dispensers may also be used. It is to be understood thatthe dispensing system 36 may be operable to dispense the same solutionto all sensing members 14, or different solutions to two or more of thesensing members 14.

The laser source 38 may be a light source that has a narrow spectralline width, and is selected to emit monochromatic light beams L withinthe visible range or within the near-infrared range. The laser source 38is positioned downstream from where the dispensing system 36 is locatedin the direction that the flexible substrate 12 is indexed. Thepositioning of the light source 38 with respect to the dispensing system36 may be far enough to enable dispensed droplets to begin evaporation,while being close enough to supply heat to increase droplet mobility.For example, the laser source 38 may supply heat to the substrate 12 anddroplets, thereby facilitating heating up of the droplet, drying of thedroplet, and subsequent pillar collapsing due to capillary forcesproduced by wetting the surface of the polygon assemblies 16. The lasersource 38 may be selected from a steady state laser or a pulsed laser.The laser source 32 is positioned to project the light L onto thevarious sensing members 14. The example shown in FIG. 8 is a VCSEL(vertical cavity surface emitting light) array that exposes an entirerow of sensing members 14 to be exposed to light L simultaneously. Inother examples, the laser source 38 may be selected to interrogate asingle sensing member 14 at a time, or multiple rows of sensing members14 at the same time. As such, parallel sensing may be performed. A lens(not shown) and/or other optical equipment (e.g., optical microscope)may be used to direct (e.g., bend) the laser light L in a desiredmanner. In one example, the laser source 38 is integrated on a chip. Thelaser source 38 may also be operatively connected to a power supply (notshown),

During operation of the system 100, flexible substrate 12 may be indexedfrom a distribution point 42 to a receiving point 44. As the flexiblesubstrate 12 is indexed, the dispensing system 36 may be operated todispense one or more samples (containing analyte(s) of interest) intodesired sensing members 14. The dispensing system 36 may be programmedto dispense into each row, every other row, or in any other desirableconfiguration.

As the flexible substrate 12 is indexed, the dispensed samples begin toevaporate, thereby collapsing the signal amplifying structures 18 withineach sensing member 14 that has been exposed to a sample, and capturinganalytes in the collapsed structures. When sensing members 14 that havereceived samples are adjacent to the light source 38, the laser source38 is operated to emit light L toward the respective sensing members 14.The analyte molecules trapped in or concentrated at or near the signalamplifying structures 18 of the sensing members 14 interact with andscatter the light/electromagnetic radiation L (note that the scatteredlight/electromagnetic radiation is labeled R). The interactions betweenthe analyte molecules and the signal amplifying material 22 (shown inFIG. 8) of the signal amplifying structures 18 cause an increase in thestrength of the Raman scattered radiation R. The Raman scatteredradiation R is redirected toward the photodetector 40, which mayoptically filter out any reflected components and/or Rayleigh componentsand then detect an intensity of the Raman scattered radiation R for eachwavelength near the incident wavelength.

Indexing of the flexible substrate 12 may be continuous so that the SERSanalysis occurs without interruption for a desired period of time, or itmay be pulsed so that indexing and SERS analysis takes place for apredetermined time, followed by another predetermined time where noindexing and no SERS analysis takes place. The electronics operating thesensing system 100 may be programmed to perform the desired continuousor periodic monitoring. The sensing system 100 could be used to performa sensing operation on demand.

Additionally, as shown in FIG. 8, the system 100 and sensor 10 allow fordispensing into one row to take place while interrogation and detectiontake place in another row that already received a dispensed sample. Thisconfiguration allows contributes to the ability for continuousmonitoring to take place. While not shown, it is to be understood thatthe system 100 may include an electronic mechanism or a mechanicalmechanism that rotates the distribution point (e.g., spool) 42 torelease additional flexible substrate 12 and unused sensing members 14while the receiving point (e.g., spool) 44 rotates in the same directionto wind up the spent portion of the integrated sensor 10. In oneexample, the continuous homogeneous indexing is performed. In anotherexample, during indexing headers of new datasets may be written withsome cataloguing information.

While not shown, it is to be understood that the system 100 may includea light filtering element positioned between the sensing members 14 andthe photodetector 40. This light filtering element may be used tooptically filter out any Rayleigh components, and/or any of the Ramanscattered radiation R that is not of a desired region. The system 100may also include a light dispersion element positioned between thesensing members 14 and the photodetector 40. The light dispersionelement may cause the Raman scattered radiation R to be dispersed atdifferent angles. The light filtering and light dispersion elements maybe part of the same device or may be separate devices.

Hardware 46, 46′, programming 48, or combinations thereof may also beoperatively connected to the dispensing system 36, the laser source 38and the photodetector 40 to control these components 36, 38, 40. Whilenot shown, hardware 46, 46′ and/or programming 48 may also beoperatively connected to the distribution point 42 and the receivingpoint 44 in order to cause the movement of the integrated sensor 10.

The same or different hardware 46, 46′ may receive readings from thephotodetector 40, and cause the same or different associated programming48 to produce a Raman spectrum readout, the peaks and valleys of whichare then utilized for analyzing the analyte molecules. The hardware 46,46′ may include memory device(s) that can store data transmitted theretofor subsequent retrieval, analysis, review, creation of a library ordatabase, etc.

The hardware 46 and/or programming 48 may be part of a device 52 that isdirectly connected to the components 36, 38, 40. Additionally oralternatively, hardware 46 and/or programming 48 may be part of a cloudcomputing system 54. Local hardware 46 and/or associated programming 48may be desirable to operate the dispensing system 36, the laser source38 and the photodetector 40, and the cloud computing system 54 may bedesirable for data storage and performing applications with such data.

The cloud computing system 54 is a computing system that includesmultiple pieces of hardware 46, 46′ operatively coupled over a networkso that they can perform a specific computing task (e.g., running thesystem 100 components, receiving data from the detector 40, enabling auser to access and/or manipulate stored SERS data, statisticalinformation, etc., and/or enabling a user to perform pre- and post-dataprocessing, anomaly detection, trend emergence/breakdown, jumps in thedata, etc.). The cloud hardware may include a combination of physicalhardware 46 (e.g., processors, servers, memory, etc.), software (i.e.,associated programming 48), and virtual hardware 46′. In an example, thecloud 54 may be configured to (i) receive requests from a multiplicityof users through application client devices 56, and (ii) return requestresponses, in the examples disclosed herein, the requests may relate toretrieval of SERS data, budding of a SERS library utilizing the user'sstored data, etc.

Physical hardware 46 may include processors, memory devices, andnetworking equipment. Virtual hardware 46′ is a type of software that isprocessed by physical hardware 46 and designed to emulate specificsoftware. For example, virtual hardware 46′ may include a virtualmachine, i.e. a software implementation of a computer that supportsexecution of an application like a physical machine. An application, asused herein, refers to a set of specific instructions executable by acomputing system for facilitating carrying out a specific task. Forexample, an application may take the form of a web-based tool providingusers with a specific functionality, e.g., retrieving previously savedSERS data. Software 48 is a set of instructions and data configured tocause virtual hardware 46′ to execute an application. As such, the cloud54 can make a particular application related to the sensing system 100available to users through client devices 56.

The hardware 46, 46′, programming 48, or combinations thereof may beimplemented in a variety of fashions. For example, the programming 48may be processor executable instructions stored on tangible,non-transitory computer readable memory media, and the hardware 46 mayinclude a processor for executing those instructions. The memory media(e.g., hard drive, memory maintained by a server, portable medium suchas a CD, DVD, or flash drive, etc.), may be used to store theinstructions that, when executed by the processor, allow a user toaccess data sent to the memory media from the detector 40. In anexample, the memory media is integrated in the same device as theprocessor, or it may be separate from, but accessible to that device andprocessor.

Referring now to FIG. 9, another example of the sensing system 100′ isdepicted. In this example, the integrated sensor 10 is incorporated intoa cassette 58. The cassette 58 includes a housing that contains theintegrated sensor 10 therein. The housing may be formed of any suitablematerial, including, for example, a polymeric material.

The cassette 58 also includes the distribution point/spool 42 and thereceiving point/spool 44 therein. The integrated sensor 10 is initiallywound on the distribution point/spool 42 and is also attached to thereceiving point/spool 44. Upon being indexed, the integrated sensor 10moves from the distribution point 42 to the receiving point 44. Thecassette may also include ropers 60 that assist in the indexing of theflexible substrate 12 from the distribution point/spool 42 to thereceiving point/spool 44 during operation. The cassette 58 may includeholes in the housing that enable respective rotating prongs to engagethe distribution point/spool 42 and the receiving point/spool 44 inorder to advance the flexible substrate 12 from the distributionpoint/spool 42 to the receiving point/spool 44.

The cassette 58 may also include an aperture 62 formed therein. Theapertures 62 are formed in one side of the housing to expose the indexedflexible substrate 12 and the sensing members 14 formed thereon to thevarious components, e.g., 36, 38, 40, etc. of the sensing system 100′ asthe integrated sensor 10 is indexed. One aperture 62 may be includedthat is large enough to expose the desirable number of sensing members14, or, as shown in FIG. 9, multiple apertures 62 may be formed acrossfrom the respective components 36, 38, 40, etc. of the sensing system100′.

While not shown, it is to be understood that the sensing system 100′itself may including a housing with a slot to receive the cassette 58and to move the cassette 58 into and out of the operating position. Sucha housing of the system 100′ may also include mechanical and/orelectrical components to advance the integrated sensor 10 in the propermanner and initiate, for example, the dispensing system 36, the lasersource 38, and the detector 40 when it is desirable to perform a sensingoperation.

As described in reference to FIG. 8, the dispenser 36, laser source 38,and detector 40 are positioned to dispense, then interrogate and detectin that order. While not shown, it is to be understood that this sensingsystem 100′ may also include the hardware 46, 46′ and/or programming 48for operating the components of the system 100′ and/or storing datareceived from the detector 40.

This example of the sensing system 100′ also includes other systems,such as a pressure sensing system 64 and a temperature analysis system66. The pressures sensing system 64 measures the pressure of the system100′ and the temperature analysis system 66 measures the temperature ofthe system 100′. The pressure sensing system 64 and/or the temperatureanalysis system 66 is a separate unit to measure environmentalcharacteristics complementary to the measurements taken by the SERScomponents. It is believed that other sensing systems may be included,such as a flow sensor to help debug system errors, for example,dispenser 36 malfunction. It is to be understood that these additionalsystems are integrated into the sensing system 100′ as separatecomponents in addition to the SERS components (e.g., dispenser 36, lasersource 38, detector 40). They may be useful to perform other desirableprocesses in addition to SERS. It is to be understood that theseadditional sensors may be operatively coupled to whatever hardware 46,46′ and/or programming 48 is utilized to operate the system 100′.

The integrated sensors 10, 10′, 10″, and 10′″ disclosed herein may beused to perform continuous or periodic monitoring of one sample ormultiple samples. The controlled patterns of polygon assemblies 16within each sensing member 14 on the flexible substrate 12 provides,over a large area, unique signal amplifying structures 18 that arecapable of trapping analytes in hot spots to enhance SERS fields andsignals.

It is to be understood that the ranges provided herein include thestated range and any value or sub-range within the stated range. Forexample, a range from about 400 nm to about 600 nm should be interpretedto include not only the explicitly recited limits of about 400 nm toabout 600 nm, but also to include individual values, such as 415 nm, 480nm, 550 nm, etc., and sub-ranges, such as from about 425 nm to about 500nm, from about 450 nm to about 575 nm, etc. Furthermore, when “about” isutilized to describe a value, this is meant to encompass minorvariations (up to +/−10%) from the stated value.

While several examples have been described in detail, it will beapparent to those skilled in the art that the disclosed examples may bemodified. Therefore, the foregoing description is to be considerednon-limiting.

What is claimed is:
 1. An integrated sensor, comprising: a substrate;and a sensing member formed on a surface of the substrate, the sensingmember including: collapsible signal amplifying structures; and an areasurrounding the collapsible signal amplifying structures that enablesself-positioning of droplets exposed thereto toward the collapsiblesignal amplifying structures.
 2. The integrated sensor as defined inclaim 1 wherein the area surrounding the collapsible signal amplifyingstructures is more hydrophobic than the collapsible signal amplifyingstructures.
 3. The integrated sensor as defined in claim 2 wherein thearea surrounding the collapsible signal amplifying structures includes agradient of polymer pillars formed on the substrate, the gradient ofpolymer pillars being more dense at a periphery of the sensing member.4. The integrated sensor as defined in claim 3 wherein: the collapsiblesignal amplifying structures include metal-capped polymer-pillars,metal-coated polymer nanoflakes, metal-coated mushroom-shapedstructures, or metal-ringed polymer pillars; and the polymer pillars inthe gradient are free of signal amplifying material.
 5. The integratedsensor as defined in claim 2 wherein the area surrounding thecollapsible signal amplifying structures includes hydrophobic moleculesdeposited thereon.
 6. The integrated sensor as defined in claim 1wherein the area surrounding the collapsible signal amplifyingstructures includes grooves defined in the surface of the substrate, thegrooves having a shape that directs the droplets toward the collapsiblesignal amplifying structures.
 7. The integrated sensor as defined inclaim 1 wherein: the collapsible signal amplifying structures arecontrollably positioned in a predetermined shape to form a polygonassembly; and the sensing member includes an array of polygon assembliesarranged in a controlled pattern.
 8. The integrated sensor as defined inclaim 1 wherein the integrated sensor includes a plurality of spacedapart sensing members.
 9. A sensing system, comprising: the integratedsensor as defined in claim 1; a sensing device to receive the integratedsensor and to index the substrate from a distribution point to areceiving point, the sensing device, including: a dispensing system todispense a sample on the sensing member as the substrate is indexed; alaser source to project light onto the sensing member after it has beenexposed to the sample; a detector to detect a signal emitted after thesensing member has been exposed to the light; and a processoroperatively connected to the detector.
 10. The sensing system as definedin claim 9 wherein the processor is a component of a cloud computingsystem.
 11. A method for using the integrated sensor as defined in claim1, the method comprising: exposing the area of the sensing member to asample in the form of the droplets, whereby the area causes the dropletsto move toward the collapsible signal amplifying structures, and whereincapillary forces from the droplets cause the collapsible signalamplifying structures to collapse; enabling the droplets to evaporate;and performing a sensing operation at the sensing member.
 12. The methodas defined in claim 11, further comprising increasing mobility of thedroplets by exposing the integrated sensor to heat or ultrasound.
 13. Amethod for making an integrated sensor, comprising: creating a sensingmember on a surface of a substrate by: forming a plurality ofcollapsible signal amplifying structures on the surface; and modifying apredefined area of the surface surrounding the collapsible signalamplifying structures so that the predefined area enablesself-positioning of droplets exposed thereto toward the collapsiblesignal amplifying structures.
 14. The method as defined in claim 13wherein the modifying of the predefined area is accomplished by: i)forming a gradient of polymer pillars on the surface, wherein thegradient of polymer pillars is more dense at a periphery of the sensingmember; ii) depositing hydrophobic molecules on the predefined area; oriii) forming a plurality of grooves in the surface, the grooves having ashape that directs the droplets toward the collapsible signal amplifyingstructures.
 15. The method as defined in claim 13 wherein forming theplurality of collapsible signal amplifying structures is accomplishedby: forming a plurality of polymer pillars, polymer nanoflakes, orpolymer mushroom-shaped structures via nanoimprinting, embossing, orroll-to-roll processing; and depositing a signal amplifying material onat least a portion of each of the plurality of polymer pillars, polymernanoflakes, or polymer mushroom-shaped structures.